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How To Purify Alcohol Using Distillation

Purifying Denatured Ethanol

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This is an example of a simple setup for distillation.

This is an example of a simple setup for distillation.

Pearson Scott Foresman, public domain
This is the chemical structure of ethanol.

This is the chemical structure of ethanol.

Benjah-bmm27/PD

Denatured alcohol is toxic to drink and may be unsuitable for some lab experiments or other purposes. If you need pure ethanol (CH3CH2OH), you can purify denatured, contaminated or impure alcohol using distillation. Here's how to do it.

Materials

  • balance
  • 100-mL volumetric flask or graduated cylinder
  • distillation apparatus
  • 250-mL beaker (or other container, to receive the distilled alcohol)
  • hotplate or other flameless heat source (to avoid igniting the ethanol)
  • boiling chips
  • 200-mL impure ethanol (e.g., 70% denatured alcohol)
If you don't have a distillation apparatus or else aren't sure what one looks like, I have instructions for making one.

Alcohol Distillation Procedure

  1. Put on appropriate safety gear, including goggles, gloves and protective clothing.

     

  2. Weigh the volumetric flask or graduated cylinder and record the value. This will help you determine your yield, if you care to calculate it.

     

  3. Add 100.00 mL of alcohol to the volumetric flask. Weigh the flask plus alcohol and record the value. Now, if you subtract the mass of the flask from this value, you will know the mass of your alcohol. The density of your alcohol is the mass per volume, which is the mass of the alcohol (the number you just obtained) divided by the volume (100.00 mL). You now know the density of the alcohol in g/mL.

     

  4. Pour the ethanol into the distillation vessel and add the remaining alcohol.

     

  5. Add a boiling chip or two to the flask.

     

  6. Assemble the distillation apparatus. The 250-mL beaker is your receiving vessel.

     

  7. Turn on the hotplate and heat the ethanol to a gentle boil. If you have a thermometer in the distillation apparatus, you'll see the temperature climb and then stabilize when it reaches the temperature of the ethanol-water vapor. Once you reach it, do not allow the temperature to exceed the stable value. If the temperature starts to climb again, it means the ethanol is gone from the distillation vessel. At this point, you could add more of the impure alcohol, if it didn't all fit in the container at the start.

     

  8. Continue distillation until you have collected at least 100 mL in the receiving beaker.

     

  9. Allow the distillate (liquid you collected) to cool to room temperature.

     

  10. Transfer 100.00 mL of this liquid into the volumetric flask, weigh the flask plus alcohol, subtract the weight of the flask (from earlier), and record the mass of the alcohol. Divide the mass of the alcohol by 100 to get the density of your distillate in g/mL. You can compare this value against a table of values to estimate the purity of your alcohol. The density of pure ethanol around room temperature is 0.789 g/mL.

     

  11. If you want, you can run this liquid through another distillation to increase its purity. Keep in mind, some alcohol is lost during every distillation, so you'll have a lower yield with the second distillation and even less final product if you do a third distillation. If you double or triple distill your alcohol, you can determine its density and estimate its purity using the same method outlined for the first distillation.

Notes About Alcohol

Ethanol is sold in the pharmacy sections of stores as a disinfectant. It may be called ethyl alcohol, ethanol or ethyl rubbing alcohol. Another common type of alcohol used for rubbing alcohol is isopropyl alcohol or isopropanol. These alcohols have different properties (notably, isopropyl alcohol is toxic), so if it matter which one you need, be sure the desired alcohol is listed on the label. Hand sanitizer gels also often use ethanol and/or isopropanol. The label should list which type of alcohol is used under the "active ingredients".

Notes About Purity

Distilling denatured alcohol will remove enough impurities for may lab applications. Further purification steps could include passing the alcohol over activated carbon. This would be especially helpful if the point of the distillation is to obtain drinkable ethanol. Be very careful distilling ethanol to drink using denatured alcohol as a source. If the denaturing agent was simply an additive intended to make the alcohol bitter, this purification might be fine, but if toxic substances were added to the alcohol, a lesser degree of contamination may remain in the distilled product. This is especially likely if the contaminant had a boiling point close to that of the ethanol. You can reduce contamination by discarding the first bit of ethanol that is collected and the last portion. It also helps to tightly control the temperature of the distillation. Just be aware: distilled alcohol is not suddenly pure! Even commercially produced ethanol still contains traces of other chemicals.

Learn More

How To Distill Ethanol from Corn or Grain
Difference Between Alcohol and Ethanol
What Is the Chemical Formula of Ethanol?
What Is Fermentation?

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